The invention concerns a control system for influencing the speed of a motor vehicle.
It is known that trucks may be equipped with the two systems:
retarder with additional function "constant speed"--RCS (regulation to constant speed by means of retarder control), and PA1 automatic speed limitation--ASL (the internal combustion is throttled down as a presettable maximum value is exceeded).
The employment of both systems is such that both operate autarchically--RCS for downhill travel and ASL in traction operation. With appropriate setpoint selection by the operator, notably on more severe grades, activating the retarder with the function "constant speed" causes the maintenance of the speed desired by the operator.
In traction operation (=engine operation), i.e., at level, uphill travel or also a light grade with the engine preferably idling and thus displaying a slight engine braking action and natural retardation, the automatic speed limitation (ASL) causes the maintenance of a fixed or variable preset maximum speed.
The system for automatic speed limitation in traction operation is comprised of a regulator and a servomechanism acting on the internal combustion engine, notably on the fuel dosing device (throttle plate or fuel injection). A limit value prescribed by law or other speed value meant not to be exceeded (maximum speed allowed) is either stored fixed in the regulator or freely selectable by the operator and storable in the regulator. The actual value input of the regulator is coupled to a measuring device that measures the actual speed of the vehicle, respectively the speed of rotation of the wheels. A continual comparison takes place between the current actual value and the speed value which is not to be exceeded (preset maximum speed). As long as the current actual speed remains below the preset maximum speed, a call for a higher speed made by the operator, for instance on the gas pedal, is converted to a control signal for the fuel dosing system. However, when the current actual speed is higher than the selected preset maximum speed, a regulating system for maintaining the preset maximum speed is activated, and the regulation enjoys a greater priority than the speed control by means of gas pedal input. In this case, the variation between actual and preset maximum speed is converted to a control signal for the servomechanism, which acts directly on the fuel dosing system of the internal combustion engine. The latter is throttled down until the limit value of the preset maximum speed is no longer exceeded. In downhill travel, the system of automatic speed limitation can be effective until the control range, which normally covers the working range of the internal combustion engine, is exhausted.
Components required for realization of the ASL function are a controller, respectively a regulator, and a pertaining servomember, respectively a servomechanism, for adjustment of the fuel dosing system of the internal combustion engine or, more generally, of the power output member of a drive engine. The servomechanism is either of strictly electromechanical design, for instance an electric servomotor, or of electropneumatic design, that is, in the form of an electropneumatic valve with pertaining servocylinder.
The retarder system with the function "constant speed" allows only manual activation by operator intervention. For realization of this task, a controller and a servomechanism in the form of a proportional valve are coordinated with the retarder. However, the controller and servomechanism are also required for realization of further control tasks that can be realized by means of the retarder and employed as well in a motor vehicle with ASL system. These tasks include the setting of a specific braking moment, the setting of a constant braking moment, and of a constant retardation.
Both systems serve to influence the travel speed, but they may be effective in different states of operation of the vehicle. Owing to the existence of two control, respectively regulating, systems--one for throttling the engine down as a presettable maximum speed value is exceeded, and a second one for control of the retarder--a large number of necessary system components are involved, translating to high linkage expense and requiring installation space. The great number of system components entails a very high probability of failure of one of the two systems by failure of system components.
The problem underlying the invention is to avoid the existing drawbacks when both systems are present, such as by integrating both systems in the vehicle in such a way that a reduction in the total number of system components is accomplished, thereby lowering the failure probability of the systems, and also precluding error sources.